Help me understand hot water supply vs. 2021 IPC charts

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millsryno

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I'm probably not understanding something correctly here, so please educate me. I've looked and looked and can't find the info.

I'm remodeling my house and trying my best to make sure I do everything right. So rather than just assume I need to loop a 3/4 hot water supply line off my 50 gallon electric water heater (has 3/4 input and output with recirc pump), I pulled up the 2021 IPC and calculated out my WSFU and cross referenced that to the distribution pipe size chart.

I calculate this water heater needs to supply 16.2 hot WSFU. This is from 3 bathroom groups (1.5 hot WSFU each, 4.5 total), laundry room (2 hot WSFU from washing machine and dog wash station that uses a shower hand wand), sink in a pantry (1 hot WSFU), kitchen (includes two sinks and two D/W- total 4.8 hot WSFU), powder room lavatory (0.5 hot WSFU), in-law suite kitchenette (includes sink and D/W - total 2.4 hot WSFU) and in-law washing machine (1 hot WSFU).

When I look at table E104.1 for water meters, mains and distribution piping size for 50-60 psi, am I supposed to reference the column for distribution pipe to determine what size line is needed for a trunk? I can't find a definition for distribution pipe and I am assuming it means the trunk line or in this case the hot water loop. Is this correct? There is one line on the table for 3/4" distribution pipe and it shows only 9.5 WSFU (max). Going by this chart I would need to upsize to 1" distribution pipe if I had 150' or less of developed length. I probably have about that.

With the water heater only having a 3/4" outlet, wouldn't that cause a bottleneck and essentially nullify the added ability of the 1" line to supply the hot water? Interestingly, my perception is that I only see 3/4" hot water trunk/loop lines being used in my area and then downsized to 1/2" to the fixtures. I must not be looking at this correctly. Please educate me.
 

millsryno

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Scottsdale, AZ
I'm probably not understanding something correctly here, so please educate me. I've looked and looked and can't find the info.

I'm remodeling my house and trying my best to make sure I do everything right. So rather than just assume I need to loop a 3/4 hot water supply line off my 50 gallon electric water heater (has 3/4 input and output with recirc pump), I pulled up the 2021 IPC and calculated out my WSFU and cross referenced that to the distribution pipe size chart.

I calculate this water heater needs to supply 16.2 hot WSFU. This is from 3 bathroom groups (1.5 hot WSFU each, 4.5 total), laundry room (2 hot WSFU from washing machine and dog wash station that uses a shower hand wand), sink in a pantry (1 hot WSFU), kitchen (includes two sinks and two D/W- total 4.8 hot WSFU), powder room lavatory (0.5 hot WSFU), in-law suite kitchenette (includes sink and D/W - total 2.4 hot WSFU) and in-law washing machine (1 hot WSFU).

When I look at table E104.1 for water meters, mains and distribution piping size for 50-60 psi, am I supposed to reference the column for distribution pipe to determine what size line is needed for a trunk? I can't find a definition for distribution pipe and I am assuming it means the trunk line or in this case the hot water loop. Is this correct? There is one line on the table for 3/4" distribution pipe and it shows only 9.5 WSFU (max). Going by this chart I would need to upsize to 1" distribution pipe if I had 150' or less of developed length. I probably have about that.

With the water heater only having a 3/4" outlet, wouldn't that cause a bottleneck and essentially nullify the added ability of the 1" line to supply the hot water? Interestingly, my perception is that I only see 3/4" hot water trunk/loop lines being used in my area and then downsized to 1/2" to the fixtures. I must not be looking at this correctly. Please educate me.
Can anybody enlighten me?
 
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